THEME B: CONTROL OF GROWTH AND MORPHOGENESIS (Anne Calof, Theme Leader) I Epithelia are organized sheets of cells that play a central role in determining the sizes and 3D architectures of our organs. Ducts, lobules, buds, alveoli, even stem cell niches, all take their form through the actions of epithelia during development. During the past grant period, through studies of the mouse olfactory epithelium OE), we made great progress in understanding how negative feedback control of self-renewal is used to achieve robust size homeostasis and rapid regeneration [19-24]. This strategy solves some of the problems that epithelia face, but not others, such as control of planar expansion; creation of morphogenetic units; and protection of cell lineages from accumulated damage. Here we take up these questions, returning to the OE, but also introducing two new systems: the mouse intestinal epithelium (IE) and the C. elegans gonad.